Android: "Expression expected" when passing an Activity class

Issue

I am kind of new to Android programming and Java in general, and I cannot work out what is causing this error; as I understand it this should work. In the code shown below (near the end of the first snippet), the line "ColourOutput.do_output((Activity) com.(name-removed).(app-name-removed).ColourActivity);" is giving the error "Expression expected" on the text "com.(name-removed).(app-name-removed).ColourActivity" in Android Studio 1.1.0.

(This is inside the class "public class ColourActivity extends Activity".)

        private Camera.PreviewCallback preview_callback = new Camera.PreviewCallback() {
        @Override
        public void onPreviewFrame(byte[] data, Camera camera) {
            int width = mCamera.getParameters().getPreviewSize().width;
            int height = mCamera.getParameters().getPreviewSize().height;
            int raw_pixels[];
            int pixels[];

            raw_pixels = new int[width * height];
            pixels = new int[get_sample_width() * get_sample_height()];
            convert_yuv(raw_pixels, data, width, height);
            crop_pixels(raw_pixels, pixels, width, height, (width - get_sample_width()) / 2, (height - get_sample_height()) / 2, get_sample_width(), get_sample_height());

            if (PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("use_mean", true) == true) {
                ColourOutput.add_colour_to_output(
                        ColourTools.get_mean(
                                pixels, get_sample_width(), get_sample_height(),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("detect_secondary", true),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("detect_white", true),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("detect_brightness", true),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getInt("quantization_secondary", 32),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getInt("quantization_dark", 43),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getInt("quantization_light", 128),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("quantization_matching_only", true)
                        ),
                        ColourOutput.ColourType.MEAN);
            }
            if (PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("use_mode", true) == true) {
                ColourOutput.add_colour_to_output(
                        ColourTools.get_mode(
                                pixels, get_sample_width(), get_sample_height(),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("detect_secondary", true),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("detect_white", true),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("detect_brightness", true),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getInt("quantization_secondary", 32),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getInt("quantization_dark", 43),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getInt("quantization_light", 128),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("quantization_matching_only", true)
                        ),
                        ColourOutput.ColourType.MODE);
            }
            ColourOutput.do_output((Activity) com.(name-removed).(app-name-removed).ColourActivity);
        }
    };

Here is the definition of "ColourOutput.do_output":

public class ColourOutput {
    private static boolean output_clear = true;
    private static String output_buffer = "";

    public static enum ColourType {
        MEAN,
        MODE
    }

    public static void add_colour_to_output(ColourTools.ColourDescription colour, ColourType type) {
        if (output_clear == true) {
            output_buffer = colour.Brightness.toString() + " " + colour.Colour.toString();
        }
        else {
            output_buffer = output_buffer + " " + colour.Brightness.toString() + " " + colour.Colour.toString();
        }
        output_clear = false;
    }

    public static void do_output(Activity activity) {
        ((TextView) activity.findViewById(R.id.output_text)).setText(output_buffer);
        output_buffer = "";
        output_clear = true;
    }
}

Solution

The error message should be self-explanatory: ...ColourActivity is a class name and a class name by itself is not a valid expression in Java. This is not an android problem, this is a simple syntax error.

do_output() expects an instance of an Activity. I'm not quite sure, what you where trying to achieve by trying to pass the name of the activity class.

I'd assume, that --since you are calling do_output() from inside your activity-- you might want to try

ColourOutput.do_output(ColorActivity.this);

instead.

As suggested by @Priya Singhal, the explicit reference to ColorActivity.this is necessary as you are calling the method from within an inner class and this refers to the instance of that inner class.

Answered By - dhke